Effect of intravenous nitroglycerin on the sublingual microcirculation in patients admitted to the intensive cardiac care unit

Introduction

Nitroglycerin (NTG), a nitric oxide donor with vasodilating effects, is frequently administered to patients with heart failure. We tested the hypothesis of whether the vasodilating effects of NTG could be monitored at the bedside.

Methods

We included heart failure patients who were admitted to the intensive cardiac care unit. In each patient, continuous NTG infusion (2 mg/hour) was started immediately after an intravenous NTG loading dose of 0.5 mg. Using side-stream dark-field imaging, sublingual microvascular perfusion was evaluated before NTG administration (T0, baseline), 2 minutes after the NTG loading dose (T1) and 15 minutes after T1 (T2). At least three video sequences of the microcirculation were recorded and analyzed. Microscan Analysis Software was used to measure the functional capillary density (FCD), an indicator of tissue perfusion. Capillaries were defined as the microvessels with a diameter <25 μm. Each value is represented as the median and interquartile range (P25–P75).

Results

Seven patients were included in this study. The mean arterial pressure decreased during execution of the study protocol: 80 (78–85) mmHg at baseline versus 75 (66–79) mmHg at T2; P = 0.03. There was a nonsignificant trend to an increase in FCD throughout the study (10.9 (9.0–12.5) μm^-1 at T0 vs 12.3 (11.3–14.0) μm^-1 at T2; P = 0.06).

Conclusion

We observed a trend to increasing FCD values during NTG treatment, despite a temporary decrease in the mean arterial pressure. This finding suggests improvement of microvascular perfusion by low-dose, intravenously administered NTG. Based on these interim results, more patients will be included in the study for final analysis and conclusions.